reverse_geocode日本の緯度経度（世界測地系、10 進）から、一番近い町字の代表点を近い順に返します（都道府県・市区町村・大字・町・丁目・小字、代表点の緯度経度、距離）。代表点で探すので、境界の近くでは隣の町字になることがあります。結果を表示するときは「出典：デジタル庁 アドレス・ベース・レジストリ（CC BY 4.0）を加工して作成」と添えてください。
| Name | Required | Description | Default |
|---|---|---|---|
| lat | Yes | 緯度（例: 35.681236） | |
| lon | Yes | 経度（例: 139.767125） | |
| limit | No | 近い順に返す件数（既定 1） |
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already establish read-only, idempotent, closed-world behavior. The description adds useful behavioral context: results are based on representative points, nearby boundaries may yield adjacent town/aza results, and attribution is required when displaying output. It does not mention rate limits or pagination, but those are minor here.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is front-loaded with the core behavior, then quickly covers the representative-point caveat and required attribution. Every sentence adds value, and there is no redundant filler.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a read-only geocoding tool with no output schema, the description explains the returned address fields, ordering, distance, boundary caveat, and attribution requirement. An agent has enough information to call and present results correctly.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 100%, with lat, lon, and limit already documented including examples, bounds, and meaning. The description adds that coordinates are decimal and based on the world geodetic system, but otherwise relies on the schema for parameter details.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description states a specific verb and resource: it returns the nearest town/aza representative points from Japanese latitude/longitude, including address components, coordinates, and distance. It is clear what the tool does, though it does not explicitly differentiate itself from the sibling lookup_zipcode tool.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
Usage is implied by the input and output description, but there is no explicit guidance on when to use this tool versus alternatives such as lookup_zipcode. The boundary caveat is helpful but does not address tool selection.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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